1. Technical Field
This invention relates to high definition television and to a method and apparatus for converting without loss of picture information a television format to and from a given recorder/player format, and more particularly to a method and apparatus for converting a first television format to and from a second television format with an improved luminance signal-to-noise ratio.
2. Related Information
Prior to the introduction in the United States and Japan of the existing NTSC standard television signal format and the introduction in Europe of the PAL and SECAM formats, there was considerable discussion over which broadcast black and white format to choose. Some broadcast formats were desirable because they exhibited less RF interference when transmitted. Other broadcast formats were desirable because they delivered a television picture having a sharper or less choppy image. Discussion again occurred, upon the introduction of color television, over which color signal broadcast format to choose and whether the chosen color format should be compatible with the broadcast black and white television format. In the United States today, the same issues are again being raised over the choice of a second generation television format--commonly known as high definition television (HDTV) or advanced television (ATV). Recent issues include discussion concerning which format is best suited for conventional over-the-air broadcast as well as best suited for transmission over new mediums such as fiber optic cable, coaxial cable, telephonic, broadcast satellite, and pre-recorded mediums. The recent issues include discussion of whether the new HDTV format should be compatible with the present NTSC format. While the Federal Communications Commission of the United States would like the new format to be NTSC compatible, there is considerable influence world-wide to adopt a totally new standard. The discussion further includes the issue of whether a proposed format will be adversely affected during broadcast or transmission on the new mediums and whether such a proposed format will subjectively provide an adequate picture. Many formats have been proposed for adoption by proponents both inside and outside the United States.
The Advanced Television Test Center was established in Alexandria, Va., as a neutral test center for evaluation and comparison of proposed HDTV formats. Besides testing the proposed HDTV formats for immunity to electrical interference and other impairments and testing for NTSC compatibility, the proposed HDTV formats are shown to viewers for subjective evaluation. Viewers compare, by psycho-physical testing, the proposed HDTV formats and rate them as to their characteristics with and without transmission impairments. In order to perform testing on all proposed formats, the television test center has a need for a uniform video tape recorder which can record all proposed source formats.
Such a uniform video source may be provided by a video tape recorder capable of recording any one of all proposed HDTV formats and playing back in the recorded HDTV format. Several digital video tape recorders (DVTR), for example, the Sony HDD-1000 and the Hitachi DVTR, are capable of recording or playing back a HDTV signal. Either the Sony or the Hitachi video tape recorder is capable of recording 1920 bytes of luminance data at 74.25 megabytes per second and two chrominance data components comprising another 1920 bytes per line at 74.25 megabytes per second as packets of data. Digital data packets are recorded at a rate of 1035 lines per frame with each frame having 2 fields. The HDD-1000 has a field rate of 60 Hz at which 74.25 megabytes per second are recorded as mentioned above. The HDD-1000 can also be used at a field rate of 59.94 Hz at which 74.175 megabytes per second are recorded. The field rate of 59.94 Hz is actually 60.times.(1000/1001) Hz. While a DVTR is capable of recording and playing back in accordance with the above-described input/output specifications, a requirement remains to provide an interface for such a recorder allowing other source formats to be recorded uniformly without the introduction of losses.
Prior systems have been proposed for recording at least one format on a single video tape recorder. For example, U.S. Pat. No. 4,549,224, issued to Nakamura et al., provides an apparatus for recognizing either an NTSC or a PAL/SECAM format and generating an appropriate recording frequency dependent on the recognized format. The Nakamura system is incapable of recording proposed high definition television formats. Furthermore, the Nakamura system does not perform signal conversion for recording or playback in a desired format.
Systems are also known for providing conversion between television formats. Many systems, however, are incapable of converting television formats without loss or alteration of picture quality. At the Advanced Television Test Center, conversion between formats must occur without alteration of picture quality or loss of information content. All known conversion systems use interpolation techniques and approximation algorithms for this type of conversion. For instance, U.S. Pat. No. 4,587,556, issued to Collins, discloses a television standard converter for converting conventional PAL and NTSC signals using weighing factors and interpolation. Furthermore, U.S. Pat. No. 4,276,565, issued to Dalton et al., converts conventional television formats using interpolation. U.S. Pat. No. 4,658,284, issued to Kawamura et al., is capable of downsizing a 625 line PAL format to a 525 line format for printing on a color printer. Interpolation is used for the downsizing conversion. Conversion between conventional formats is also performed in U.S. Pat. No. 4,661,862 issued to Thompson, wherein data reduction is performed by deletion and in U.S. Pat. No. 4,283,736, issued to Morio et at., wherein conversion by discarding or repeating information signals is performed. Such schemes entail loss in picture quality or content. Interpolation itself is a faltering function. Some information must be lost and therefore such schemes cannot be truly bi-directional.
Other systems such as that disclosed in U.S. Pat. No. 4,743,958, issued to Bannister et al., convert conventional encoded NTSC, PAL, SECAM and analog RGB, YUV to separate chrominance and luminance signals for input to a special effects device. Bannister et al. performs the conversion using filters for processing the signals. U.S. Pat. No. 4,463,387, issued to Hashimoto et al., processes video data both before recording and after playback for quality improvement. No conversion is performed.
Systems for adapting an input to a VCR include U.S. Pat. No. 4,597,020, issued to Wilkinson, wherein a video signal is shuffled before recording and unshuffled upon playback to disburse bursts of errors. U.S. Pat. No. 4,530,048, issued to Proper, adapts a VCR for computer memory backup storage. Proper concerns interfacing a VCR to avoid VCR information dropouts, a problem of no concern for digital video recording. U.S. Pat. No. 4,638,380, issued to Wilkinson et al., discloses a multiple head video tape recorder with switching and interpolation to remove the effects of a failed head.
Yet another system disclosed in U.S. Pat. No. 4,797,746 to Ashcraft is directed to a system for converting digital image information in a storage format to a format such as a digital scan converter format or standard television format. The disclosed system includes a high bit rate interface unit (HBRI) comprising an input controller, an image buffer RAM, an output controller and a system controller. The HBRI receives stored data from a storage device, such as a tape unit or an optical disk, and based on commands output from the system controller, converts the received data to another format. The system controller commands control the input controller as to the location in the image buffer RAM where each data point or bit is read. The output controller is responsive to the commands of the system controller for reading out each data point from the image buffer RAM so that a standard digital scan converter format or television format is produced.
U.S. Pat. No. 4,577,240 to Hedberg et al. relates to a system capable of on-line acquisition, processing and display of radiographs and for off-line recording, retrieval, review, image processing and archival storage of images. The disclosed system includes word formatter circuits which convert incoming digital data having a width of between 6 and 10 bits into a sequence of 5 separate data streams for recording into a centralized library. The word formatter circuits are used in playback to convert the recorded data for display by HDTV direct imaging or fluoroscopy to produce from quality images.
U.S. Pat. No. 4,651,208 was issued to Charles Rhodes, the inventor of the present application, and was assigned to an assignee other than the assignee of the present application. The patent discloses conversion between widescreen and non-widescreen television transmissions using input/output multiplexers for line conversion in line memory pairs. Picture lines are clocked into and out of a memory to change the aspect ratio of a picture from a large to a small picture aspect ratio. The process is not bi-directional because side panel pixels are discarded when a wide aspect ratio image, such as 16:9, is converted to a less wide aspect ratio image, such as 4:3. Afterwards, the reduced aspect ratio image cannot be reconverted back to the original wide aspect ratio image.
None of the above systems provide a uniform video source for equally comparing proposed high definition television formats. Known interpolators and filters unfortunately reproduce and convert high definition television signals with the sacrifice of picture information. While the invention disclosed in aforementioned U.S. Pat. No. 4,651,208 to Rhodes relates to a method and apparatus for converting widescreen television signals for display on non-widescreen television displays, the process is irreversible and does not facilitate video recording.